1. Field of the Invention
This invention relates to a method for measuring pressures, and more specifically, to a method for measuring pressures using microcapsules containing a substantially colorless color former (an electron donating organic compound) capable of forming a color image on contact with a color developer (an electron accepting material).
2. Description of the Prior Art
Dynamic measuring methods for various pressures of, e.g., a planar and linear nature, have gained increasing importance in recent years. Yet no simple method for measuring these pressures is known, and those methods now available involve complicated procedures. Pressures desired to be measured by such methods include, for example, the clamping pressure of bolts in machinery in general, the pressurization of automotive brakes, the pressure of molds, the mold clamping pressure, the bonding pressure between the mold wall and the resin in the mold, the molding pressure within the mold in thermoplastic and thermosetting resin fabrications, the contacting pressure of springs, the clamping planar pressures of joints of carburetors, fuel pipes, fuel tanks, etc. in fuel systems, the colliding pressure between the human body and other objects in an automobile collision, the linear and planar pressures of rubber and plastic rolls, the effective limit and effectiveness of gasket seals, the hydraulic pressure in brakes, the teeth containing pressure of gears, the planar contact pressure between solids, the contacting pressure of a cock in a cock valve, the contacting pressure between curved surfaces, the contacting pressure of rolls for steel materials during operation, the pressure between the sole of a persons foot and the floor surface, and the pressure between the human body and chairs.
Conventional pressure measuring methods, for example, involve the use of a strain gauge utilizing the relationship between stress and strain, the use of a load meter, or the use of a pressure-sensitive paint (lacquers sensitive to strain).
The use of strain gauges for the measurement of planar and linear pressures, however, requires not only various devices such as an amplifier, detector or recorder, but also techniques for operating them and complicated calculation involving material dynamics. Furthermore, this method has the defect that the material to be measured must have a smooth surface. Strain gauges are described in detail, for example, in J. Yarnell, STRAIN GAUGE published by Electronic Engineering Co., Ltd. (London), 1951.
The method using a pressure-sensitive paint suffers from the disadvantage of coating non-uniformity and unsatisfactory adhesiveness, and requires a complicated operation.
A load meter, on the other hand, cannot be made small in size, and the method using it is unsuitable for measurement of planar and linear pressures.
A method is also known in which a pressure-sensitive laminate is used as disclosed in U.S. Pat. No. 3,647,504. This U.S. Patent discloses a single sheet-type recording paper containing marking liquids of different colors contained in microcapsules with different wall thicknesses. Since different capsules are ruptured when different pressures are applied, the colors of the ruptured capsules naturally differ. The degree of the pressure applied can thus be evaluated from the color obtained. This method makes it possible to evaluate pressures qualitatively, but it is difficult to calculate accurately the pressures measured. Furthermore, a large amount of coloration is formed with the pressure-sensitive laminate and thus, the hands or clothes are soiled.